In recent years significant advances have been made in controllable flight kite and related airfoil technology, beginning in the 1940's with two-line kites that allowed for the first time a significant degree of flight control, and culminating within the last few years in four-line, or quad-line, kites that permit precision flying. This invention relates to an improved quad-line kite with exceptional balance of control, maneuverability at roughly equivalent speed in any direction, rotation about its axis in either direction, and flight capability in especially light winds.
Early development of kite control can be traced to Paul Garber, who in 1944 developed the Navy Target Kite (U.S. Pat. No. 2,388,478) which was maneuvered via two lines. This kite was flown from shipboard to serve as a gunnery target. A variety of two line kites for recreational use followed, represented in popular versions by the Peter Powell (U.S. Pat. Nos. 3,954,235 and 4,076,189), a two-line kite shaped like a traditional diamond kite, and the Flexifoil (U.S. Pat. No. 4,129,272), a two-line kite shaped like an aerofoil and inflated by wind pressure from the front.
In the most recent development, a number of four-line, or quad-line, kites have been marketed. These kites in general exhibit a remarkable degree of precision flying and control by means of the four control lines. Typical examples of these quad-line kites that are available include models with names such as "Revolution" (U.S. Pat. No. 4,892,272), "Omni" (Stunt Kite Quarterly Magazine, back cover, Fall/Winter 1991), and "Tetrad" (American Kite Magazine, p.45, Summer 1991). All are significant advancements over two-line kites in terms of their ability to be rotated or flown in various directions at the operator's command via the four lines.
The available quad-line kites, while substantially advanced over the prior art of two-line kites, nevertheless do have limitations. These limitations generally relate to the ability of the kite to move in various directions. For this purpose, it is helpful to understand that the edge of the kite connected to lines attached to the upper ends of the control handles (as they are held by the operator) is generally considered to be the "front" of the kite. Therefore, when the kite in question is moving in the direction of that edge, it can be said to be moving "forward". Movement in the opposite direction of that edge is generally termed "reverse."
The Revolution is advertised by its manufacturers as being capable of "forward and reverse flight." No mention is made of the possibility of sideways flight. Experienced operators are able to cause the kite to fly directly sideways, but this maneuver is not achievable by non-experts. However, even in the hands of an expert, the rate of sideways flight is markedly slower than the rate of forward flight. Also, it is difficult to maintain the Revolution in motion once sideways flight has begun. In addition, the rate of reverse flight is much slower than the rate of forward flight. Thus, the Revolution falls short of the ideal kite which would have the ability to fly with stability in all directions at equal speed.
To address this problem, two other manufacturers have devised quad-line kites. The Tetrad is advertised to provide flight "in all directions." In this respect its manufacturer has succeeded. The Tetrad is maneuverable in all directions by quad-line operators of average ability. However, the rates of sideways and forward/reverse flight are not equal, and the kite is unacceptably slow in all directions. The Tetrad is also difficult to accelerate smoothly from a hovering position into flight in a given direction. Additionally, it is difficult to cause the Tetrad to continue moving with stability in any direction once movement has begun.
The Omni also advertises "performance in all directions." Like the Tetrad, the Omni is maneuverable in all directions by operators of average ability. Also like the Tetrad, the Omni exhibits a resistance to beginning motion in a given direction. The Omni is capable of stable sideways motion, but forward and reverse flight are difficult to maintain. Most importantly, however, the Omni's rates of movement are not equal. In contrast with the Revolution, which moves fastest in a forward direction, the Omni is much faster in the sideways direction than in forward or reverse.
In all of the above cases, there is an instability in motion or a resistance to motion that is manifested by the kite twisting slightly and moving in a direction other than the desired one. Another universal problem is the excessive weight of the spars relative to the sail area of the kite. This hinders the ability of the kites to fly in low wind. Finally, each of the above kites has a limitation in its ability to move as quickly in one direction as it can in others. Therefore, in summary, the available quad-line kites (1) do not exhibit the desired ability to easily begin and maintain flight in all directions, (2) do not exhibit the desired ability to fly in low wind, and (3) do not exhibit the desired ability to move with equal speed in any direction.